In a substrate processing apparatus for performing plasma etching or the like on a semiconductor wafer, components made of various materials are provided in a processing chamber where the semiconductor wafer is accommodated. Some of the components are worn by a plasma. Therefore, there are suggested various methods that measure a wear amount of a component to check replacement timing of the worn component.
For example, there is suggested a method for measuring a wear amount of a focus ring based on a thickness of the focus ring which is measured by using interference between reflected light from a front surface of the focus ring and reflected light from a rear surface of the focus ring in the case of irradiating low-coherence light in a thickness direction of the focus ring in a processing chamber (see, e.g., Japanese Patent Application Publication No. 2008-227063). The method disclosed in Japanese Patent Application Publication No. 2008-227063 utilizes principle that an optical path difference between the reflected light from the front surface and the reflected light from the rear surface of the component to which the low-coherence light is irradiated is changed by thermal expansion depending on a temperature of the component. There is also suggested a method for measuring a temperature of a component by using low-coherence light based on the above principle (see, e.g., Japanese Patent Application Publication No. 2006-220461).
The wear amount measuring method disclosed in Japanese Patent Application Publication No. 2008-227063 and the temperature measuring method disclosed in Japanese Patent Application Publication No. 2006-220461 can be applied to a component made of a material, e.g., Si, which transmits a wavelength of the low-coherence light. However, such methods cannot be used for measuring a thickness or wear amount and a temperature of a component made of a material, e.g., ceramic or the like, which does not transmit the low-coherence light.
Therefore, it is general to take out a ceramic member as a measurement target component from the processing chamber and measure a thickness or wear mount thereof by using a three-dimensional measuring device. In addition, there is suggested an ultrasonic diffraction method used for measuring a thickness of a ceramic film formed on a surface of a ceramic member (see, Japanese Patent Application Publication No. 2004-333366).
However, the thickness measurement using the three-dimensional measurement device or the thickness measurement using ultrasonic diffraction method is a contact-type measuring method and thus cannot be used in a state where the ceramic member is disposed in the processing chamber. In that case, it is required to expose the inside of the processing chamber to the atmosphere, take out the ceramic member from the processing chamber, measure a thickness of the ceramic member at the outside of the chamber, return the ceramic member into the processing chamber after the thickness measurement, and depressurize the inside of the processing chamber to a vacuum state. Accordingly, the operating rate of the substrate processing apparatus is considerably decreased. Further, a temperature of a ceramic member provided in a processing chamber cannot be measured by the three-dimensional measuring device or the ultrasonic diffraction method.